But as the past two cycles have shown, rules are made to be broken. So now, it’s time to get into the weeds to see where the two parties stand at the beginning of a cycle that undoubtedly has many twists and turns ahead of it.

Democrats need to net 17 seats next year to reach a 218-seat majority in the House.

Democratic operatives identify 30 House Republicans who won by less than 10 points last year and assert that the margin makes them vulnerable in 2014. But the GOP incumbents who won by less than 10 points didn’t start, or end, at the same place last cycle.

For example, Republican Rep. Tom Latham of Iowa defeated another incumbent, Democrat Leonard L. Boswell, running in territory very different from the Republican’s district last decade. Because of that, Latham’s 8-point victory — in a district that President Barack Obama won by more than 4 points — is a sign of strength, not vulnerability.

Similarly, Republican Rep. Steve King’s 8-point victory in another Iowa district over a highly touted Democrat isn’t a sign of vulnerability. King beat Christie Vilsack, wife of the former governor and current secretary of Agriculture, by almost the identical margin that Mitt Romney beat Obama in the district, suggesting a polarized electorate with a clear Republican bent.

North Carolina GOP Rep. Richard Hudson knocked off Democratic Rep. Larry Kissell by “only” 7.9 points, but that hardly suggests a great opportunity for Democrats next year in a district that Romney won by about 17 points.

After looking over the list of 30 Republicans who won by less than 10 points, I see no more than 11 who deserve to be on a list of initially vulnerable GOPers. But let’s be generous and add Minnesota Rep. Michele Bachmann (who is likely to again win a narrow victory) to the list, bringing it to an even dozen.

To that dozen, add two California districts held by Republicans that voted for Obama — currently represented by David Valadao and Gary G. Miller — that the GOP won either because of a Democratic recruiting problem or the state’s runoff process. Given the fundamentals of Miller’s district, his seat is a Democratic takeover waiting to happen.

That makes 17 districts where Democrats start with realistic opportunities to make gains. The list could grow, of course, with GOP retirements, unusually strong Democratic recruits or redrawn districts in Florida and Texas. But 17 districts are not nearly enough opportunities to give Democrats a decent chance of taking back the House.